Quantitative determination of odanacatib in human plasma using liquid–liquid extraction followed by liquid chromatography–tandem mass spectrometry analysis

Odanacatib (ODN, MK-0822) is an investigational drug under development for the treatment of osteoporosis. A quantitative LC/MS–MS methodology was developed and validated to determine ODN concentrations in human plasma, with a linear calibration range from 0.500 to 500 ng/mL. Stable isotope 13C6-labeled ODN was employed as the internal standard (IS). Sample preparation was based on liquid–liquid extraction of basified plasma with methyl t-butyl ether in a 96-well plate format. The extracted samples were analyzed on a liquid chromatography–tandem mass spectrometry system equipped with a turbo ion spray source. Chromatographic separation of the analyte and IS was achieved on a Phenomenex Luna C18 (50 mm × 2.0 mm, 5 μm) column. Ion pairs m/z 526 → 313 for the analyte and m/z 532 → 319 for the IS were monitored in positive ionization mode for MS detection. This methodology has been fully validated and proved to be rugged and reproducible. Intra- and inter-run variability was within 5.88%, with accuracy between 95.6 and 106% of the nominal concentrations. Analyte stability was evaluated under various sample preparation, analysis and storage conditions. This assay has been utilized to analyze human plasma samples obtained from phase I to III clinical trials.